- All Implemented Interfaces:
Runnable
- Direct Known Subclasses:
ForkJoinWorkerThread
Thread
defines constructors and a Thread.Builder
to create threads.
Starting a thread schedules it to execute its run
method. The newly started thread executes concurrently with the thread that caused
it to start.
A thread terminates if either its run
method completes normally,
or if its run
method completes abruptly and the appropriate uncaught exception handler completes normally or
abruptly. With no code left to run, the thread has completed execution. The
join
method can be used to wait for a thread to terminate.
Threads have a unique identifier and a name. The identifier is generated when a Thread
is created
and cannot be changed. The thread name can be specified when creating a thread
or can be changed at a later time.
Threads support ThreadLocal
variables. These are variables that are
local to a thread, meaning a thread can have a copy of a variable that is set to
a value that is independent of the value set by other threads. Thread
also
supports InheritableThreadLocal
variables that are thread local variables
that are inherited at thread creation time from the parent Thread
.
Thread
supports a special inheritable thread local for the thread
context-class-loader.
Platform threads
Thread
supports the creation of platform threads that are
typically mapped 1:1 to kernel threads scheduled by the operating system.
Platform threads will usually have a large stack and other resources that are
maintained by the operating system. Platforms threads are suitable for executing
all types of tasks but may be a limited resource.
Platform threads get an automatically generated thread name by default.
Platform threads are designated daemon or non-daemon threads.
When the Java virtual machine starts up, there is usually one non-daemon
thread (the thread that typically calls the application's main
method).
The shutdown sequence begins when all started
non-daemon threads have terminated. Unstarted non-daemon threads do not prevent
the shutdown sequence from beginning.
In addition to the daemon status, platform threads have a thread priority and are members of a thread group.
Virtual threads
Thread
also supports the creation of virtual threads.
Virtual threads are typically user-mode threads scheduled by the Java
runtime rather than the operating system. Virtual threads will typically require
few resources and a single Java virtual machine may support millions of virtual
threads. Virtual threads are suitable for executing tasks that spend most of
the time blocked, often waiting for I/O operations to complete. Virtual threads
are not intended for long running CPU intensive operations.
Virtual threads typically employ a small set of platform threads used as
carrier threads. Locking and I/O operations are examples of operations
where a carrier thread may be re-scheduled from one virtual thread to another.
Code executing in a virtual thread is not aware of the underlying carrier thread.
The currentThread() method, used to obtain a reference
to the current thread, will always return the Thread
object
for the virtual thread.
Virtual threads do not have a thread name by default. The getName
method returns the empty string if a thread name is not set.
Virtual threads are daemon threads and so do not prevent the shutdown sequence from beginning. Virtual threads have a fixed thread priority that cannot be changed.
Creating and starting threads
Thread
defines public constructors for creating platform threads and
the start
method to schedule threads to execute. Thread
may be extended for customization and other advanced reasons although most
applications should have little need to do this.
Thread
defines a Thread.Builder
API for creating and starting both
platform and virtual threads. The following are examples that use the builder:
Runnable runnable = ...
// Start a daemon thread to run a task
Thread thread = Thread.ofPlatform().daemon().start(runnable);
// Create an unstarted thread with name "duke", its start() method
// must be invoked to schedule it to execute.
Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);
// A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
// Start a virtual thread to run a task
Thread thread = Thread.ofVirtual().start(runnable);
// A ThreadFactory that creates virtual threads
ThreadFactory factory = Thread.ofVirtual().factory();
Inheritance when creating threads
AThread
inherits its initial values of inheritable-thread-local variables (including the context class loader) from
the parent thread values at the time that the child Thread
is created.
The 5-param constructor can be used to create a thread that does not inherit its initial
values from the constructing thread. When using a Thread.Builder
, the
inheritInheritableThreadLocals
method can be used to select if the initial values are inherited.
Platform threads inherit the daemon status, thread priority, and when not provided (or not selected by a security manager), the thread group.
Creating a platform thread captures the
caller context to limit the permissions of the new thread when it executes code that performs a privileged action. The captured
caller context is the new thread's "Inherited AccessControlContext
". Creating
a virtual thread does not capture the caller context; virtual threads have no
permissions when executing code that performs a privileged action.
Unless otherwise specified, passing a null
argument to a constructor
or method in this class will cause a NullPointerException
to be thrown.
- Implementation Note:
- In the JDK Reference Implementation, the virtual thread scheduler may be configured
with the following system properties:
System property Description jdk.virtualThreadScheduler.parallelism
The number of platform threads available for scheduling virtual threads. It defaults to the number of available processors. jdk.virtualThreadScheduler.maxPoolSize
The maximum number of platform threads available to the scheduler. It defaults to 256. - Since:
- 1.0
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic interface
A builder forThread
andThreadFactory
objects.static enum
A thread state.static interface
Interface for handlers invoked when aThread
abruptly terminates due to an uncaught exception. -
Field Summary
Modifier and TypeFieldDescriptionstatic final int
The maximum priority that a thread can have.static final int
The minimum priority that a thread can have.static final int
The default priority that is assigned to a thread. -
Constructor Summary
ConstructorDescriptionThread()
Initializes a new platformThread
.Initializes a new platformThread
.Initializes a new platformThread
.Initializes a new platformThread
.Thread
(ThreadGroup group, Runnable task) Initializes a new platformThread
.Thread
(ThreadGroup group, Runnable task, String name) Initializes a new platformThread
so that it hastask
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
.Thread
(ThreadGroup group, Runnable task, String name, long stackSize) Initializes a new platformThread
so that it hastask
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
, and has the specified stack size.Thread
(ThreadGroup group, Runnable task, String name, long stackSize, boolean inheritInheritableThreadLocals) Initializes a new platformThread
so that it hastask
as its run object, has the specifiedname
as its name, belongs to the thread group referred to bygroup
, has the specifiedstackSize
, and inherits initial values for inheritable thread-local variables ifinheritThreadLocals
istrue
.Thread
(ThreadGroup group, String name) Initializes a new platformThread
. -
Method Summary
Modifier and TypeMethodDescriptionstatic int
Returns an estimate of the number of live platform threads in the current thread's thread group and its subgroups.final void
Deprecated, for removal: This API element is subject to removal in a future version.This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release.protected Object
clone()
Throws CloneNotSupportedException as a Thread can not be meaningfully cloned.int
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally designed to count the number of stack frames but the results were never well-defined and it depended on thread-suspension.static Thread
Returns the Thread object for the current thread.static void
Prints a stack trace of the current thread to the standard error stream.static int
Copies into the specified array every live platform thread in the current thread's thread group and its subgroups.static Map
<Thread, StackTraceElement[]> Returns a map of stack traces for all live platform threads.Returns the contextClassLoader
for this thread.Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception.long
getId()
Deprecated.This method is not final and may be overridden to return a value that is not the thread ID.final String
getName()
Returns this thread's name.final int
Returns this thread's priority.Returns an array of stack trace elements representing the stack dump of this thread.getState()
Returns the state of this thread.final ThreadGroup
Returns the thread's thread group ornull
if the thread has terminated.Returns the handler invoked when this thread abruptly terminates due to an uncaught exception.static boolean
Returnstrue
if and only if the current thread holds the monitor lock on the specified object.void
Interrupts this thread.static boolean
Tests whether the current thread has been interrupted.final boolean
isAlive()
Tests if this thread is alive.final boolean
isDaemon()
Tests if this thread is a daemon thread.boolean
Tests whether this thread has been interrupted.final boolean
Returnstrue
if this thread is a virtual thread.final void
join()
Waits for this thread to terminate.final void
join
(long millis) Waits at mostmillis
milliseconds for this thread to terminate.final void
join
(long millis, int nanos) Waits at mostmillis
milliseconds plusnanos
nanoseconds for this thread to terminate.final boolean
Waits for this thread to terminate for up to the given waiting duration.static Thread.Builder.OfPlatform
Returns a builder for creating a platformThread
orThreadFactory
that creates platform threads.static Thread.Builder.OfVirtual
Returns a builder for creating a virtualThread
orThreadFactory
that creates virtual threads.static void
Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities.final void
resume()
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally specified to resume a thread suspended withsuspend()
.void
run()
This method is run by the thread when it executes.void
Sets the contextClassLoader
for this thread.final void
setDaemon
(boolean on) Marks this thread as either a daemon or non-daemon thread.static void
Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.final void
Changes the name of this thread to be equal to the argumentname
.final void
setPriority
(int newPriority) Changes the priority of this thread.void
Set the handler invoked when this thread abruptly terminates due to an uncaught exception.static void
sleep
(long millis) Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers.static void
sleep
(long millis, int nanos) Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers.static void
Causes the currently executing thread to sleep (temporarily cease execution) for the specified duration, subject to the precision and accuracy of system timers and schedulers.void
start()
Schedules this thread to begin execution.static Thread
startVirtualThread
(Runnable task) Creates a virtual thread to execute a task and schedules it to execute.final void
stop()
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally specified to "stop" a victim thread by causing the victim thread to throw aThreadDeath
.final void
suspend()
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally specified to suspend a thread.final long
threadId()
Returns the identifier of this Thread.toString()
Returns a string representation of this thread.static void
yield()
A hint to the scheduler that the current thread is willing to yield its current use of a processor.
-
Field Details
-
MIN_PRIORITY
public static final int MIN_PRIORITYThe minimum priority that a thread can have.- See Also:
-
NORM_PRIORITY
public static final int NORM_PRIORITYThe default priority that is assigned to a thread.- See Also:
-
MAX_PRIORITY
public static final int MAX_PRIORITYThe maximum priority that a thread can have.- See Also:
-
-
Constructor Details
-
Thread
public Thread()Initializes a new platformThread
. This constructor has the same effect as Thread(null, null, gname)
, wheregname
is a newly generated name. Automatically generated names are of the form"Thread-"+
n, where n is an integer.This constructor is only useful when extending
Thread
to override therun()
method.- See Also:
-
Thread
Initializes a new platformThread
. This constructor has the same effect as Thread(null, task, gname)
, wheregname
is a newly generated name. Automatically generated names are of the form"Thread-"+
n, where n is an integer.For a non-null task, invoking this constructor directly is equivalent to:
Thread.ofPlatform().unstarted(task);
- Parameters:
task
- the object whoserun
method is invoked when this thread is started. Ifnull
, this classesrun
method does nothing.- See Also:
-
Thread
Initializes a new platformThread
. This constructor has the same effect as Thread(group, task, gname)
, wheregname
is a newly generated name. Automatically generated names are of the form"Thread-"+
n, where n is an integer.For a non-null group and task, invoking this constructor directly is equivalent to:
Thread.ofPlatform().group(group).unstarted(task);
- Parameters:
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group.task
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked.- Throws:
SecurityException
- if the current thread cannot create a thread in the specified thread group- See Also:
-
Thread
Initializes a new platformThread
. This constructor has the same effect as Thread(null, null, name)
.This constructor is only useful when extending
Thread
to override therun()
method.- Parameters:
name
- the name of the new thread- See Also:
-
Thread
Initializes a new platformThread
. This constructor has the same effect as Thread(group, null, name)
.This constructor is only useful when extending
Thread
to override therun()
method.- Parameters:
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group.name
- the name of the new thread- Throws:
SecurityException
- if the current thread cannot create a thread in the specified thread group- See Also:
-
Thread
Initializes a new platformThread
. This constructor has the same effect as Thread(null, task, name)
.For a non-null task and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform().name(name).unstarted(task);
- Parameters:
task
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked.name
- the name of the new thread- See Also:
-
Thread
Initializes a new platformThread
so that it hastask
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
.If there is a security manager, its
checkAccess
method is invoked with the ThreadGroup as its argument.In addition, its
checkPermission
method is invoked with theRuntimePermission("enableContextClassLoaderOverride")
permission when invoked directly or indirectly by the constructor of a subclass which overrides thegetContextClassLoader
orsetContextClassLoader
methods.The priority of the newly created thread is the smaller of priority of the thread creating it and the maximum permitted priority of the thread group. The method setPriority may be used to change the priority to a new value.
The newly created thread is initially marked as being a daemon thread if and only if the thread creating it is currently marked as a daemon thread. The method setDaemon may be used to change whether or not a thread is a daemon.
For a non-null group, task, and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform().group(group).name(name).unstarted(task);
- Parameters:
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group.task
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked.name
- the name of the new thread- Throws:
SecurityException
- if the current thread cannot create a thread in the specified thread group or cannot override the context class loader methods.- See Also:
-
Thread
Initializes a new platformThread
so that it hastask
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
, and has the specified stack size.This constructor is identical to
Thread(ThreadGroup,Runnable,String)
with the exception of the fact that it allows the thread stack size to be specified. The stack size is the approximate number of bytes of address space that the virtual machine is to allocate for this thread's stack. The effect of thestackSize
parameter, if any, is highly platform dependent.On some platforms, specifying a higher value for the
stackSize
parameter may allow a thread to achieve greater recursion depth before throwing aStackOverflowError
. Similarly, specifying a lower value may allow a greater number of threads to exist concurrently without throwing anOutOfMemoryError
(or other internal error). The details of the relationship between the value of thestackSize
parameter and the maximum recursion depth and concurrency level are platform-dependent. On some platforms, the value of thestackSize
parameter may have no effect whatsoever.The virtual machine is free to treat the
stackSize
parameter as a suggestion. If the specified value is unreasonably low for the platform, the virtual machine may instead use some platform-specific minimum value; if the specified value is unreasonably high, the virtual machine may instead use some platform-specific maximum. Likewise, the virtual machine is free to round the specified value up or down as it sees fit (or to ignore it completely).Specifying a value of zero for the
stackSize
parameter will cause this constructor to behave exactly like theThread(ThreadGroup, Runnable, String)
constructor.Due to the platform-dependent nature of the behavior of this constructor, extreme care should be exercised in its use. The thread stack size necessary to perform a given computation will likely vary from one JRE implementation to another. In light of this variation, careful tuning of the stack size parameter may be required, and the tuning may need to be repeated for each JRE implementation on which an application is to run.
Implementation note: Java platform implementers are encouraged to document their implementation's behavior with respect to the
stackSize
parameter.For a non-null group, task, and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform().group(group).name(name).stackSize(stackSize).unstarted(task);
- Parameters:
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group.task
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked.name
- the name of the new threadstackSize
- the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.- Throws:
SecurityException
- if the current thread cannot create a thread in the specified thread group- Since:
- 1.4
- See Also:
-
Thread
public Thread(ThreadGroup group, Runnable task, String name, long stackSize, boolean inheritInheritableThreadLocals) Initializes a new platformThread
so that it hastask
as its run object, has the specifiedname
as its name, belongs to the thread group referred to bygroup
, has the specifiedstackSize
, and inherits initial values for inheritable thread-local variables ifinheritThreadLocals
istrue
.This constructor is identical to
Thread(ThreadGroup,Runnable,String,long)
with the added ability to suppress, or not, the inheriting of initial values for inheritable thread-local variables from the constructing thread. This allows for finer grain control over inheritable thread-locals. Care must be taken when passing a value offalse
forinheritThreadLocals
, as it may lead to unexpected behavior if the new thread executes code that expects a specific thread-local value to be inherited.Specifying a value of
true
for theinheritThreadLocals
parameter will cause this constructor to behave exactly like theThread(ThreadGroup, Runnable, String, long)
constructor.For a non-null group, task, and name, invoking this constructor directly is equivalent to:
Thread.ofPlatform() .group(group) .name(name) .stackSize(stackSize) .inheritInheritableThreadLocals(inheritInheritableThreadLocals) .unstarted(task);
- Parameters:
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group.task
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked.name
- the name of the new threadstackSize
- the desired stack size for the new thread, or zero to indicate that this parameter is to be ignoredinheritInheritableThreadLocals
- iftrue
, inherit initial values for inheritable thread-locals from the constructing thread, otherwise no initial values are inherited- Throws:
SecurityException
- if the current thread cannot create a thread in the specified thread group- Since:
- 9
- See Also:
-
-
Method Details
-
currentThread
Returns the Thread object for the current thread.- Returns:
- the current thread
-
yield
public static void yield()A hint to the scheduler that the current thread is willing to yield its current use of a processor. The scheduler is free to ignore this hint.Yield is a heuristic attempt to improve relative progression between threads that would otherwise over-utilise a CPU. Its use should be combined with detailed profiling and benchmarking to ensure that it actually has the desired effect.
It is rarely appropriate to use this method. It may be useful for debugging or testing purposes, where it may help to reproduce bugs due to race conditions. It may also be useful when designing concurrency control constructs such as the ones in the
java.util.concurrent.locks
package. -
sleep
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.- Parameters:
millis
- the length of time to sleep in milliseconds- Throws:
IllegalArgumentException
- if the value ofmillis
is negativeInterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
-
sleep
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.- Parameters:
millis
- the length of time to sleep in millisecondsnanos
-0-999999
additional nanoseconds to sleep- Throws:
IllegalArgumentException
- if the value ofmillis
is negative, or the value ofnanos
is not in the range0-999999
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
-
sleep
Causes the currently executing thread to sleep (temporarily cease execution) for the specified duration, subject to the precision and accuracy of system timers and schedulers. This method is a no-op if the duration is negative.- Parameters:
duration
- the duration to sleep- Throws:
InterruptedException
- if the current thread is interrupted while sleeping. The interrupted status of the current thread is cleared when this exception is thrown.- Since:
- 19
-
onSpinWait
public static void onSpinWait()Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities. By invoking this method within each iteration of a spin-wait loop construct, the calling thread indicates to the runtime that it is busy-waiting. The runtime may take action to improve the performance of invoking spin-wait loop constructions.- API Note:
- As an example consider a method in a class that spins in a loop until
some flag is set outside of that method. A call to the
onSpinWait
method should be placed inside the spin loop.class EventHandler { volatile boolean eventNotificationNotReceived; void waitForEventAndHandleIt() { while ( eventNotificationNotReceived ) { Thread.onSpinWait(); } readAndProcessEvent(); } void readAndProcessEvent() { // Read event from some source and process it . . . } }
The code above would remain correct even if the
onSpinWait
method was not called at all. However on some architectures the Java Virtual Machine may issue the processor instructions to address such code patterns in a more beneficial way. - Since:
- 9
-
ofPlatform
Returns a builder for creating a platformThread
orThreadFactory
that creates platform threads.Interaction with security manager when creating platform threads
Creating a platform thread when there is a security manager set will invoke the security manager's
checkAccess(ThreadGroup)
method with the thread's thread group. If the thread group has not been set with theOfPlatform.group
method then the security manager'sgetThreadGroup
method will be invoked first to select the thread group. If the security managergetThreadGroup
method returnsnull
then the thread group of the constructing thread is used.- API Note:
- The following are examples using the builder:
// Start a daemon thread to run a task Thread thread = Thread.ofPlatform().daemon().start(runnable); // Create an unstarted thread with name "duke", its start() method // must be invoked to schedule it to execute. Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable); // A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ... ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
- Returns:
- A builder for creating
Thread
orThreadFactory
objects. - Since:
- 21
-
ofVirtual
Returns a builder for creating a virtualThread
orThreadFactory
that creates virtual threads.- API Note:
- The following are examples using the builder:
// Start a virtual thread to run a task. Thread thread = Thread.ofVirtual().start(runnable); // A ThreadFactory that creates virtual threads ThreadFactory factory = Thread.ofVirtual().factory();
- Returns:
- A builder for creating
Thread
orThreadFactory
objects. - Since:
- 21
-
clone
Throws CloneNotSupportedException as a Thread can not be meaningfully cloned. Construct a new Thread instead.- Overrides:
clone
in classObject
- Returns:
- a clone of this instance.
- Throws:
CloneNotSupportedException
- always- See Also:
-
startVirtualThread
Creates a virtual thread to execute a task and schedules it to execute.This method is equivalent to:
Thread.ofVirtual().start(task);
- Parameters:
task
- the object to run when the thread executes- Returns:
- a new, and started, virtual thread
- Since:
- 21
- See Also:
-
isVirtual
public final boolean isVirtual()Returnstrue
if this thread is a virtual thread. A virtual thread is scheduled by the Java virtual machine rather than the operating system.- Returns:
true
if this thread is a virtual thread- Since:
- 21
-
start
public void start()Schedules this thread to begin execution. The thread will execute independently of the current thread.A thread can be started at most once. In particular, a thread can not be restarted after it has terminated.
- Throws:
IllegalThreadStateException
- if the thread was already started
-
run
public void run()This method is run by the thread when it executes. Subclasses ofThread
may override this method.This method is not intended to be invoked directly. If this thread is a platform thread created with a
Runnable
task then invoking this method will invoke the task'srun
method. If this thread is a virtual thread then invoking this method directly does nothing. -
stop
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally specified to "stop" a victim thread by causing the victim thread to throw aThreadDeath
. It was inherently unsafe. Stopping a thread caused it to unlock all of the monitors that it had locked (as a natural consequence of theThreadDeath
exception propagating up the stack). If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects became visible to other threads, potentially resulting in arbitrary behavior. Usages ofstop
should be replaced by code that simply modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run method in an orderly fashion if the variable indicates that it is to stop running. If the target thread waits for long periods (on a condition variable, for example), theinterrupt
method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.ThrowsUnsupportedOperationException
.- Throws:
UnsupportedOperationException
- always
-
interrupt
public void interrupt()Interrupts this thread.Unless the current thread is interrupting itself, which is always permitted, the
checkAccess
method of this thread is invoked, which may cause aSecurityException
to be thrown.If this thread is blocked in an invocation of the
wait()
,wait(long)
, orwait(long, int)
methods of theObject
class, or of thejoin()
,join(long)
,join(long, int)
,sleep(long)
, orsleep(long, int)
methods of this class, then its interrupt status will be cleared and it will receive anInterruptedException
.If this thread is blocked in an I/O operation upon an
InterruptibleChannel
then the channel will be closed, the thread's interrupt status will be set, and the thread will receive aClosedByInterruptException
.If this thread is blocked in a
Selector
then the thread's interrupt status will be set and it will return immediately from the selection operation, possibly with a non-zero value, just as if the selector'swakeup
method were invoked.If none of the previous conditions hold then this thread's interrupt status will be set.
Interrupting a thread that is not alive need not have any effect.
- Implementation Note:
- In the JDK Reference Implementation, interruption of a thread
that is not alive still records that the interrupt request was made and
will report it via
interrupted()
andisInterrupted()
. - Throws:
SecurityException
- if the current thread cannot modify this thread
-
interrupted
public static boolean interrupted()Tests whether the current thread has been interrupted. The interrupted status of the thread is cleared by this method. In other words, if this method were to be called twice in succession, the second call would return false (unless the current thread were interrupted again, after the first call had cleared its interrupted status and before the second call had examined it).- Returns:
true
if the current thread has been interrupted;false
otherwise.- See Also:
-
isInterrupted
public boolean isInterrupted()Tests whether this thread has been interrupted. The interrupted status of the thread is unaffected by this method.- Returns:
true
if this thread has been interrupted;false
otherwise.- See Also:
-
isAlive
public final boolean isAlive()Tests if this thread is alive. A thread is alive if it has been started and has not yet terminated.- Returns:
true
if this thread is alive;false
otherwise.
-
suspend
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally specified to suspend a thread. It was inherently deadlock-prone. If the target thread held a lock on a monitor protecting a critical system resource when it was suspended, no thread could access the resource until the target thread was resumed. If the thread intending to resume the target thread attempted to lock the monitor prior to callingresume
, deadlock would result. Such deadlocks typically manifested themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.ThrowsUnsupportedOperationException
.- Throws:
UnsupportedOperationException
- always
-
resume
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally specified to resume a thread suspended withsuspend()
. Suspending a thread was inherently deadlock-prone. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.ThrowsUnsupportedOperationException
.- Throws:
UnsupportedOperationException
- always
-
setPriority
public final void setPriority(int newPriority) Changes the priority of this thread. For platform threads, the priority is set to the smaller of the specifiednewPriority
and the maximum permitted priority of the thread's thread group. The priority of a virtual thread is alwaysNORM_PRIORITY
andnewPriority
is ignored.- Parameters:
newPriority
- the new thread priority- Throws:
IllegalArgumentException
- if the priority is not in the rangeMIN_PRIORITY
toMAX_PRIORITY
.SecurityException
- ifcheckAccess()
determines that the current thread cannot modify this thread- See Also:
-
getPriority
public final int getPriority()Returns this thread's priority.The priority of a virtual thread is always
NORM_PRIORITY
.- Returns:
- this thread's priority.
- See Also:
-
setName
Changes the name of this thread to be equal to the argumentname
.First the
checkAccess
method of this thread is called with no arguments. This may result in throwing aSecurityException
.- Implementation Note:
- In the JDK Reference Implementation, if this thread is the current thread, and it's a platform thread that was not attached to the VM with the Java Native Interface AttachCurrentThread function, then this method will set the operating system thread name. This may be useful for debugging and troubleshooting purposes.
- Parameters:
name
- the new name for this thread.- Throws:
SecurityException
- if the current thread cannot modify this thread.- External Specifications
- See Also:
-
getName
Returns this thread's name.- Returns:
- this thread's name.
- See Also:
-
getThreadGroup
Returns the thread's thread group ornull
if the thread has terminated.The thread group returned for a virtual thread is the special ThreadGroup for virtual threads.
- Returns:
- this thread's thread group or
null
-
activeCount
public static int activeCount()Returns an estimate of the number of live platform threads in the current thread's thread group and its subgroups. Virtual threads are not included in the estimate.The value returned is only an estimate because the number of threads may change dynamically while this method traverses internal data structures, and might be affected by the presence of certain system threads. This method is intended primarily for debugging and monitoring purposes.
- Returns:
- an estimate of the number of live platform threads in the current thread's thread group and in any other thread group that has the current thread's thread group as an ancestor
-
enumerate
Copies into the specified array every live platform thread in the current thread's thread group and its subgroups. This method simply invokes theThreadGroup.enumerate(Thread[])
method of the current thread's thread group. Virtual threads are not enumerated by this method.An application might use the activeCount method to get an estimate of how big the array should be, however if the array is too short to hold all the threads, the extra threads are silently ignored. If it is critical to obtain every live thread in the current thread's thread group and its subgroups, the invoker should verify that the returned int value is strictly less than the length of
tarray
.Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.
- Parameters:
tarray
- an array into which to put the list of threads- Returns:
- the number of threads put into the array
- Throws:
SecurityException
- ifThreadGroup.checkAccess()
determines that the current thread cannot access its thread group
-
countStackFrames
Deprecated, for removal: This API element is subject to removal in a future version.This method was originally designed to count the number of stack frames but the results were never well-defined and it depended on thread-suspension. This method is subject to removal in a future version of Java SE.ThrowsUnsupportedOperationException
.- Returns:
- nothing
- See Also:
-
join
Waits at mostmillis
milliseconds for this thread to terminate. A timeout of0
means to wait forever. This method returns immediately, without waiting, if the thread has not beenstarted
.- Implementation Note:
- For platform threads, the implementation uses a loop of
this.wait
calls conditioned onthis.isAlive
. As a thread terminates thethis.notifyAll
method is invoked. It is recommended that applications not usewait
,notify
, ornotifyAll
onThread
instances. - Parameters:
millis
- the time to wait in milliseconds- Throws:
IllegalArgumentException
- if the value ofmillis
is negativeInterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
-
join
Waits at mostmillis
milliseconds plusnanos
nanoseconds for this thread to terminate. If both arguments are0
, it means to wait forever. This method returns immediately, without waiting, if the thread has not beenstarted
.- Implementation Note:
- For platform threads, the implementation uses a loop of
this.wait
calls conditioned onthis.isAlive
. As a thread terminates thethis.notifyAll
method is invoked. It is recommended that applications not usewait
,notify
, ornotifyAll
onThread
instances. - Parameters:
millis
- the time to wait in millisecondsnanos
-0-999999
additional nanoseconds to wait- Throws:
IllegalArgumentException
- if the value ofmillis
is negative, or the value ofnanos
is not in the range0-999999
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
-
join
Waits for this thread to terminate.An invocation of this method behaves in exactly the same way as the invocation
join
(0)
- Throws:
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
-
join
Waits for this thread to terminate for up to the given waiting duration.This method does not wait if the duration to wait is less than or equal to zero. In this case, the method just tests if the thread has terminated.
- Parameters:
duration
- the maximum duration to wait- Returns:
true
if the thread has terminated,false
if the thread has not terminated- Throws:
InterruptedException
- if the current thread is interrupted while waiting. The interrupted status of the current thread is cleared when this exception is thrown.IllegalThreadStateException
- if this thread has not been started.- Since:
- 19
-
dumpStack
public static void dumpStack()Prints a stack trace of the current thread to the standard error stream. This method is useful for debugging. -
setDaemon
public final void setDaemon(boolean on) Marks this thread as either a daemon or non-daemon thread. The shutdown sequence begins when all started non-daemon threads have terminated.The daemon status of a virtual thread is always
true
and cannot be changed by this method tofalse
.This method must be invoked before the thread is started. The behavior of this method when the thread has terminated is not specified.
- Parameters:
on
- iftrue
, marks this thread as a daemon thread- Throws:
IllegalArgumentException
- if this is a virtual thread andon
is falseIllegalThreadStateException
- if this thread is aliveSecurityException
- ifcheckAccess()
determines that the current thread cannot modify this thread
-
isDaemon
public final boolean isDaemon()Tests if this thread is a daemon thread. The daemon status of a virtual thread is alwaystrue
.- Returns:
true
if this thread is a daemon thread;false
otherwise.- See Also:
-
checkAccess
Deprecated, for removal: This API element is subject to removal in a future version.This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.Determines if the currently running thread has permission to modify this thread.If there is a security manager, its
checkAccess
method is called with this thread as its argument. This may result in throwing aSecurityException
.- Throws:
SecurityException
- if the current thread is not allowed to access this thread.- See Also:
-
toString
Returns a string representation of this thread. The string representation will usually include the thread's identifier and name. The default implementation for platform threads includes the thread's identifier, name, priority, and the name of the thread group. -
getContextClassLoader
Returns the contextClassLoader
for this thread. The contextClassLoader
may be set by the creator of the thread for use by code running in this thread when loading classes and resources. If not set, the default is to inherit the context class loader from the parent thread.The context
ClassLoader
of the primordial thread is typically set to the class loader used to load the application.- Returns:
- the context
ClassLoader
for this thread, ornull
indicating the system class loader (or, failing that, the bootstrap class loader) - Throws:
SecurityException
- if a security manager is present, and the caller's class loader is notnull
and is not the same as or an ancestor of the context class loader, and the caller does not have theRuntimePermission
("getClassLoader")
- Since:
- 1.2
-
setContextClassLoader
Sets the contextClassLoader
for this thread.The context
ClassLoader
may be set by the creator of the thread for use by code running in this thread when loading classes and resources.If a security manager is present, its
checkPermission
method is invoked with aRuntimePermission
("setContextClassLoader")
permission to see if setting the context ClassLoader is permitted.- Parameters:
cl
- the context ClassLoader for this Thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)- Throws:
SecurityException
- if the current thread cannot set the context ClassLoader- Since:
- 1.2
-
holdsLock
Returnstrue
if and only if the current thread holds the monitor lock on the specified object.This method is designed to allow a program to assert that the current thread already holds a specified lock:
assert Thread.holdsLock(obj);
- Parameters:
obj
- the object on which to test lock ownership- Returns:
true
if the current thread holds the monitor lock on the specified object.- Since:
- 1.4
-
getStackTrace
Returns an array of stack trace elements representing the stack dump of this thread. This method will return a zero-length array if this thread has not started, has started but has not yet been scheduled to run by the system, or has terminated. If the returned array is of non-zero length then the first element of the array represents the top of the stack, which is the most recent method invocation in the sequence. The last element of the array represents the bottom of the stack, which is the least recent method invocation in the sequence.If there is a security manager, and this thread is not the current thread, then the security manager's
checkPermission
method is called with aRuntimePermission("getStackTrace")
permission to see if it's ok to get the stack trace.Some virtual machines may, under some circumstances, omit one or more stack frames from the stack trace. In the extreme case, a virtual machine that has no stack trace information concerning this thread is permitted to return a zero-length array from this method.
- Returns:
- an array of
StackTraceElement
, each represents one stack frame. - Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow getting the stack trace of thread.- Since:
- 1.5
- See Also:
-
getAllStackTraces
Returns a map of stack traces for all live platform threads. The map does not include virtual threads. The map keys are threads and each map value is an array ofStackTraceElement
that represents the stack dump of the correspondingThread
. The returned stack traces are in the format specified for thegetStackTrace
method.The threads may be executing while this method is called. The stack trace of each thread only represents a snapshot and each stack trace may be obtained at different time. A zero-length array will be returned in the map value if the virtual machine has no stack trace information about a thread.
If there is a security manager, then the security manager's
checkPermission
method is called with aRuntimePermission("getStackTrace")
permission as well asRuntimePermission("modifyThreadGroup")
permission to see if it is ok to get the stack trace of all threads.- Returns:
- a
Map
fromThread
to an array ofStackTraceElement
that represents the stack trace of the corresponding thread. - Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow getting the stack trace of thread.- Since:
- 1.5
- See Also:
-
getId
Deprecated.This method is not final and may be overridden to return a value that is not the thread ID. UsethreadId()
instead.Returns the identifier of this Thread. The thread ID is a positivelong
number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime.- Returns:
- this thread's ID
- Since:
- 1.5
-
threadId
public final long threadId()Returns the identifier of this Thread. The thread ID is a positivelong
number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime.- Returns:
- this thread's ID
- Since:
- 19
-
getState
Returns the state of this thread. This method is designed for use in monitoring of the system state, not for synchronization control.- Returns:
- this thread's state.
- Since:
- 1.5
-
setDefaultUncaughtExceptionHandler
Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.Uncaught exception handling is controlled first by the thread, then by the thread's
ThreadGroup
object and finally by the default uncaught exception handler. If the thread does not have an explicit uncaught exception handler set, and the thread's thread group (including parent thread groups) does not specialize itsuncaughtException
method, then the default handler'suncaughtException
method will be invoked.By setting the default uncaught exception handler, an application can change the way in which uncaught exceptions are handled (such as logging to a specific device, or file) for those threads that would already accept whatever "default" behavior the system provided.
Note that the default uncaught exception handler should not usually defer to the thread's
ThreadGroup
object, as that could cause infinite recursion.- Parameters:
ueh
- the object to use as the default uncaught exception handler. Ifnull
then there is no default handler.- Throws:
SecurityException
- if a security manager is present and it deniesRuntimePermission
("setDefaultUncaughtExceptionHandler")
- Since:
- 1.5
- See Also:
-
getDefaultUncaughtExceptionHandler
Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception. If the returned value isnull
, there is no default.- Returns:
- the default uncaught exception handler for all threads
- Since:
- 1.5
- See Also:
-
getUncaughtExceptionHandler
Returns the handler invoked when this thread abruptly terminates due to an uncaught exception. If this thread has not had an uncaught exception handler explicitly set then this thread'sThreadGroup
object is returned, unless this thread has terminated, in which casenull
is returned.- Returns:
- the uncaught exception handler for this thread
- Since:
- 1.5
-
setUncaughtExceptionHandler
Set the handler invoked when this thread abruptly terminates due to an uncaught exception.A thread can take full control of how it responds to uncaught exceptions by having its uncaught exception handler explicitly set. If no such handler is set then the thread's
ThreadGroup
object acts as its handler.- Parameters:
ueh
- the object to use as this thread's uncaught exception handler. Ifnull
then this thread has no explicit handler.- Throws:
SecurityException
- if the current thread is not allowed to modify this thread.- Since:
- 1.5
- See Also:
-